Equal marriage has been declared legal across the US, after a Supreme Court ruling that said attempts by individual states to ban it is unconstitutional.

The ruling means that the number of states where gay marriage is legal will rise from 37 to 50. Loud cheers were heard outside the court after the ruling was announced, with one of the demonstrators, Jordan Monaghan, calling his mother from his mobile phone amid the celebrations: ‘Hey mom, I’m at the Supreme Court. Your son can have a husband now,’ he said.

Lawyers had argued that marriage was defined by law only to encourage procreation within stable family units, and therefore could only meaningfully apply to men and women. But justice Anthony Kennedy, in his ruling, said: ‘That is not to say the right to marry is less meaningful for those who do not or cannot have children. An ability, desire, or promise to procreate is not and has not been a prerequisite for a valid marriage in any State.’

Referencing the constitutional right to liberty, Kennedy added: ‘The petitioners in these cases seek to find that liberty by marrying someone of the same sex and having their marriages deemed lawful on the same terms and conditions as marriages between persons of the opposite sex.’

‘The Supreme Court’s decision is a huge victory for same-sex couples in the US that will reverberate in many countries that still deny people the right to marry the person they love,’ said Boris Dittrich, lesbian, gay, bisexual, and transgender (LGBT) rights advocacy director at Human Rights Watch. ‘It will strengthen everyone’s fundamental rights to equality and non-discrimination, irrespective of sexual orientation or gender identity.’

In addition to the four state bans that were found unconstitutional in today’s ruling, 10 other states currently retain bans on same-sex marriage. It is unclear when states retaining same-sex marriage bans will comply with the Supreme Court’s ruling and begin issuing marriage licenses to same-sex couples.

Same-sex marriage is now legal in Argentina, Belgium, Brazil, Canada, Denmark, France, Iceland, Ireland, Luxembourg, the Netherlands, New Zealand, Norway, Portugal, South Africa, Spain, Sweden, the United Kingdom and Uruguay, as well as in parts of Mexico. In May, voters in Ireland overwhelmingly approved a referendum enshrining the right to marriage equality in the country’s constitution. The law is expected to come into effect later this year.

The White House tweeted a video showing states where equal marriage has been made legal, with the words #LoveWins – and even changed their avi to a rainbow coloured White House.

Ruth Hunt, Chief Executive of Stonewall, commented: ‘This is a fantastic day for equality and with Pride events taking place all around the world this month, this news could not be more perfectly timed. Congratulations to all the happy couples who will now be able to say “I do”. There’s still a long way to go until marriage is legal for all same-sex couples across the world, but we hope that today is a sign of more good things to come.’